This invention is related to graphics controller systems and, more particularly, to graphics controller systems with low power dissipation.
As shown in FIG. 1, a typical graphics controller system has a graphics controller integrated circuit 10, which has a graphics engine 12 for manipulating video data, and a CPU interface 13, display interface 14 and video memory interface 15. The graphics controller integrated circuit 10 receives video image data from a CPU (central processing unit) through the CPU interface 13, and after processing the data, stores that information through the video memory interface 15 in a separate video memory 11, also called the video frame buffer. The graphics controller 10 also makes sure that the image data is regularly retrieved from the video memory (through the interface 15) and fed to a display unit through the display interface 14 with a frequency which satisfies the refresh requirements of the display. In some more advanced graphics controller systems, video image data may also be received from other sources, such as a device with a PCMCIA (Personal Computer Memory Card International Association) connector.
The video memory interface 15 of the graphics controller integrated circuit 10 has ports dedicated to interface with the video memory 11. The number of ports required for this interface 15 is the sum of the address, data and control signals required to access the video memory 11. The memory 111 has a size which is a function of the video frame buffer required to support the display resolution. While dynamic random access memory (DRAM) is most commonly used for the video frame buffer, some high performance systems use VRAMs (DRAMs with serial data ports added). A typical VGA (Video Graphics Adapter standard) display in an IBM-compatible mobile computer, often called a notebook computer, with an LCD (liquid crystal display) panel uses a single 256K×16 DRAM integrated circuit as a video frame buffer. A typical SVGA (Super VGA standard) system uses two such DRAMs organized as 256K×32.
Wider data paths between the video memory and the graphics controller allow greater bandwidth for data transfer. However, the wider data paths also increase the pin count of the graphics controller package and the package count of the DRAMs with the accompanying increased manufacturing complexity and costs. A 16-bit data path requires one DRAM package and approximately 30 signal lines to handle the memory address, data, and control signals, while a 32-bit data path requires two DRAM packages and 50 signal lines. Power dissipation is increased as more signal lines are added since each signal line has a parasitic capacitance associated with the package I/O pin, as well as with the conducting trace on the motherboard of the mobile computer system. Therefore, an increase in graphics performance is accompanied by an increase in power dissipation, pin count and package count.
The present invention solves or substantially mitigates these problems with a high performance graphics controller system having low power dissipation, and low pin and package counts.